Toothpaste compositions are well characterised in the literature and many compositions are disclosed in patent specifications and other literature. Toothpaste compositions contain a number of specific components for example abrasive agents, fluoride sources, binders, preservatives, humectants, anti plaque agents, colouring agents, water, flavour and other optional ingredients. Of these components the abrasive agent is required to provide the appropriate cleaning and plaque removal without subjecting the tooth itself to excessive abrasion. Typically a toothpaste composition will contain from about 5% to about 50%, preferably up to about 30%, by weight of abrasive. Commonly used abrasives are aluminas, calcium carbonates and calcium phosphates. More recently synthetic silicas have been adopted because of their efficient cleaning, compatibility with other ingredients and their physical properties.
Normally, silicas used as abrasives in toothpaste formulations have low structure as defined by their oil absorption. In general, silicas with oil absorptions less than 110 cm.sup.3 /100 g are considered to have low structure, whereas those in excess of 180 cm.sup.3 /100 g have high structure and they are usually employed as thickeners, fillers and liquid carriers.
Examples of abrasive silicas with low structure can be found in UK 1;482,354; 1,482,355 (Huber) and UK 1,264,292 (Unilever). In terms of abrasivity, the silicas disclosed in the Huber specifications would be defined as medium, whereas those described in the Unilever patent are considered high.
Medium structured silicas in the oil absorption range 110-180 cm.sup.3 /100 g have low levels of abrasivity and are normally used as structuring and polishing agents in toothpaste formulations. Examples are U.S. Pat. No. 3,864,470 (Unilever) where the product Neosyl.RTM. (typical oil absorption value 160 cm.sup.3 /100 g) is referred to as a polishing agent any UK 1501905 in which Huber describe a polishing silica with medium structure.